Wharfcreek
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Hello Forum, new guy here. Just registered, and I'm here as a result of attempting to resolve some problems with a Zen Kit build that a friend of mine did and turned over to me to 'de-bug'.
I found a thread in the Forum that addressed one issue I had, which was what I believed to be an error on the Schematic reflected as being pins 6 and 8 of the power tube where it should be pins 7 and 9. In believing this to be 'resolved', I'm moving on to another part of this, which is also on the power tube, but related to pins 1 and 3. My Schematic reflects a .1 cap across those two pins. The PC board has a location for this cap, but the board is designed for the 6P15P tube, which connects Pin 6 and pin 1 internally. So, the board's connection of this .1 cap goes between pins 1 and 6. When using a 6BQ5, there is no 'internal' connection between pin 1 and pin 6, so the connection for this cap isn't made. I'm just wondering what affect that has on the circuit, and if anyone has added a 'jumper' between pins 6 and 1 in order to complete this part of the circuit?
Next, I'm curious about the pair of 330K resistors that are on this board, but not shown on the schematic? Can anyone shed any light on what these are for/about...... and why they're on the PC board but NOT on the schematic? Should I remove them / leave them in?
Finally, I'm dealing with a bit of a 'hum' issue with this amp. In attempting to diagnose it's cause, I've determined that if the 6DJ8 tube is removed, the hum goes away. When 'in' the amp, the volume control doesn't affect the hum level any. My 'rookie' belief about this is that this indicates that the hum is not in the section of the power supply that affects the 'output' tubes, nor is it being generated from within the output tubes. I also believe this indicates it's not on the 'input' side of the AF tube (6DG8), since the Volume Control has no affect on the noise. This leaves me with either a 'filtering' issue as related to the AF tube, or some form of 'bleed' or 'inducted' noise getting to the PC board. This amp has NOT had the film cap updates to the PS filter caps as indicated on the Schematic. I'm wondering if that could be the cause? Has anyone else encountered this issue? Amp does have the 100 ohm 'virtual center tap' installed across the filament supply leads.
If anyone can address any of the above issues for me, I'd really appreciate the help!
Many thanks!! Tom D.
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